Telephone system



Nov. 2, 1 943.

5. E. PETERSON TELEPHONE SYSTEM Filed Nov. 8, 1940 10 Shets-Sheet 1 flllu i LINE cmcu/r l0 FINDER sw. I!

J E Rl/O LQ F R] 132 .1 III) [/24 90,

ll4 L732". man I CONN. BANKS [6 I /7 /6 I L/NE CIRCUIT- 20 16% 9 DISTRIBUTOR 1912i 55 1, J I 1' G9 INVENTOR SETH E. PETERSON ATTORNEYS Nov. 2, 1943. v s. E. PETERSON TELEPHONE SYSTEM Filed Nov.- 8, 1940 10 Sheets-Sheet 2 RESTRICTED SERVICE8TIME BLOCKlNG REL YS Z5 24/ j FIG! I FIG. 3 FIG. 4 FIG.6 FIG. 7 FIG. 8

FIG? F168 F7610 INVENTOR SETH E. PETERSON ATTORNEYS 1943- s E. PETERSON 2,333,489

TELEPHONE SYSTEM Filed Nov. 8, 1940 10 Sheets-Sheet 3 CONNECTOR 40 332 UNK sw/rm.

TMRU LINE SETH E. PETERSON A'II'TORNEY Nov. 2, 1943. s. E. PETERSON v 2,333,489

TELEPHONE SYSTEM I 7 Filed Nov. 8, 1940 10 Sheets-SheetA (C6! 4 6 "417 060 (16/7 E C627 CONNECTOR 40 Fin 4 4!! CALLING INVENTOR SETH E. PETERSON M QM ATTORNEYS Nov. 2, 1943. s. E. PETERSON 2,333,489

TELEPHONE SYSTEM Filed Nov. '8, 1940 10 Sheets-Sheet 5 {C6, -ceo' 53/ C6! 06/7 062 QQZ CONNECTOR 40 C678 INVENTOR SETH E. PETERSON TTORNEYS 1943- s. E. PETERSON 33,

TELEPHONE SYSTEM Filed Nov. 8, 1940 10 Sheets-Sheet 6 CONNECTOR 40 622 T/M/NG LINE SWITCH INVENTOR C80 6680 L639 C58, SETH E. PETERSON m mun M M ZTTQRNEYs Nov. 2, 1943.

5. E. PETERSON 2,333,489

TELEPHONE SYSTEM Filed Nov. 8 1940 10 Sheets-Sheet 8 CONTROL Lcres 823 Emma M (846 Hm!) 0799 PL824 L 7 8813 [C702 I 703 [j I 835 84 C757 "ow LINE CIRCUIT TO FINDER B/JNKS s 1%- LEAD LINE SWITCHING P UL S E TWO WAY REPE/ITEI? 30 D/STANT-AUTOMAT/C ExcHA NGE 35 INVENTOR SETH E. PETERSON BY ATTORNEYS Nov. 2, 1943. s. E. PETERSON TELEPHONE SYSTEM Filed Nov. 8, 1940 10 Sheets-Sheet 9 v 0677 -c494, LC678- TIME? START CIRCUITS 50 93/ r r l "fig-1 @679 I933 -v- V\IV\ Q R920 6657 ;4'\:55 I57 5 59 5- DIAL C344 {I 8/ BUSY T/CK TONE CONVERSATION PERM TONE GENERATING T/MEH TIMER GEN EQUIPMENT CIRCUIT 5/ a "52 53 INVENTOR SETH E. PETERSON ATTOR NEYS 10 Sheets-SheeE 1o s. EJPETERSON TELEPHONE SYSTEM Filed Nov. 8, 1940 I CODE SELECTING 3CONVERSATION T/M/NG SWITCH 45 INVENTOR- SETH E. PETERSON WIW I M A TORNEYs Nov. 2, 1943.

FROM 0005 SW Patented Nov. 2, 1943 UNITED STATES;

TELEPHONE SYSTEM Seth E. Peterson Cali, Colu nibia,-assignon.to Automatic Electriclaboratori'e's, 1110;, a tame Application November 8, 1940SriailN6m364324 22 Claims? (Cl. 179-47) The presentinventionrelates to telephone sys tems', and more particularly to 'improved'Iauto'-' maticline-switching equipment which is control-' lable in a'simDl-e and reliable ma'nner over Jin'es:

ofdifferent'types; such, forexam'ple; as ful1- mei--- tallic lines K of both the-100p and simplextypes; and-' groundreturn lines; to provide different. classes'oiservice to subscribers paying difierentr rates;--

According to a fu rthenoloject ofaitlieiiriventionel. the type oi rir'i g hitt-off iitiiizefl in-i terminatiri'g the' tiansmission onringingscurrentx over'a z'se'ized'c.

line'is autoinatically determmedxluringseizure*ofu 'th linci" It 'is' a further obd eff-tibia the inmcnti'on Ftoi' pmvidexs. in a -lin 'sele'ctingi switchi ,annimproved'iicimuitir arrangeme' whereby l'th'e loack=bringfeerela3t:?of

the 'swit'ohiiunctionsirbotnias aasupemsoryrsignanr Itisanobject of the invention to prOVide'i inIa .10 icontrol relay ahd tasi airingingimontroicrelay.

system-of th character described, an improved: and eXceeding-ly simple arrangement whereby the regular line-terminating equipment, individual to the lines of the-system,-is utilized to signa=1 thein a telephonley'stemofrtheicharacter descritieda; certain" restnicted triinksitwhich :are utilized": tor handle ca l ls' originatingiiatinonarestiicted stations:

automatic switching apparatus asto the type or 1finonh g 'and whieh arernaikedxagainsinseizure fromi;

cla-ssof the calling linesover whichthe apparatus-l is seized.

According to another object of the invention; Y the =1ine'-cla'ss signaling circuits are so arranged restricted-' stat i ision aniindimduahtnunk basisn.

According o-- another iobicotfiofiatherdnvention .v

the calt resti ictingr apparatusisoflithe automation switching equipmenu -is tjointly :"contmiled IOi Itt;

that extra con-trol paths' extendingthrough:theagozqm'arkiiig paths indiwtiiiaimto'rthe linesziamangeduc outlet contacts of the automatic sWitcheS arenOt' required for the transmission of the signals:

It isanother object ofthe invention to provide in a telephone systemof the character describcdnt foi re'stricted serviceg andl marking: pathsJindi-xv viduallly identifying rtheerestricteditrunksnt lt'iis anotherfiobject of the inuenti'onlto provides arnimpreveaccentierwneuwork ifOIfZ-EthEi-Il'lfilikihgi an arrangement-whereby the station sel'eetive 25i-pathsy which is so aritangeflt t 11011191101 i tne cennoi' pu1ses tnansmitted'wvenithecmarkingo are tr'arismitte over certain'oisthe marking pathsm tocontrolth service restrictin-gsapparatus:nfix the automatic-mi hingiequipmemz';

Accordihganother objectaofmzhe iriventionis pathsaremtilized ttilcontrblathemperationsrnfrthe; tin'r controlledlinkreleaserelaiys'providedlinztheis re eaters'iare eachiequipped'wvith liners testiii annaratunwhich'z ifunctidnsartorstgnal l a a seized repeater -as to thc ch'aracter 10f thescallingi: line iaverwhich' theseizd repeater-is to be con-e whereby the line circuits terminating multiparty l40w trolled fdlloiving itsseizureii subscriber lines of the ground return type are ai -'1 ranged to control the ringing control equipment: of the connector switches'in a manner such thatn ringing current'transmission over the: ground rot- In aecord'ancewith a furtheueobjemtmfrtherin-=2 venti'oni provisiens ar imadewherelzmonemf the con-troiflea'ids connecting! one: ofz stliea trunkrre-vpeaters with thehutletmontactsfiofiihemrececlinge.

turn side of a selected line .ofthis type is posi: =selectorswitches is utilizedilfonrcontnollingmthe=:

tively prevented.

It-is another obj ectof the invention :to provide"? in a telephone system of the characterdescrlbed; automatic switching equipment whichis so-ran trui'ih s ele cting operationsmfi the seie'ctor switcheee and' aiso fc r thepurpose of indi'catingntolthe sea; lectt ii switche' -th rres-trinte'dior znon restrictedxe character oi? :th EtIHHK' -tGFm'iIIBitGdbyythecle-z for terminating the transmission'of ringing ecur-':- rent over certain called lines of theisyste'm', andr.'= a :difierent ty'peof-ring cut+ofi is utilized limiters."- minating the transmission of ringingcurrent-over r other called' lines of the" system. i

Ill-3S provider for userzinn controlling; then-automation switchingiapparatustof a telephone system,vime proved ftiming e-equipmentmwhichr.isso -.am =anged :I

551 mien ther startingwof :the'equi-pment and theconI-F still fanotheirvobiect of thel-rinventioneito-vtrol of the automatic switching apparatusare exercised over a single control lead extending from the switching apparatus to the timing equipment.

In the illustrated embodiment of the invention there is provided a system which comprises a plurality of subscriber lines, certain of which are of the multiparty type individually having a plurality of substations associated therewith, and automatic switching apparatus in the form of finder-connector links for setting up connections between the lines of the system. The connector switches of the links also have access to one or more groups of trunks which are provided to serve only the substations arranged for unrestricted service and may extend, for example, to one or more distant suburban or central exchanges. Timing equipment common to the links is provided for conversation timing and for forcibly releasing links held over lines having permanent calling conditions thereon.

The subscriber lines of the system are of several different types and include lines arranged for loop circuit control of the automatic switching equipment, simplex circuit control of the automatic switching equipment, and also lines of the ground return type. These lines are individually terminated in line circuits which conventionally comprise line, cut-ofi and lockout relays. In accordance with one feature of the present invention, the cut-off and lockout relays provided in the line circuits terminating lines of the simplex and ground return types, are arranged to transmit a control pulse over the positive talking conductors of the respective associated lines when calls are initiated on these lines. A control pulse f this character, when transmitted to a link assigned to the use of a calling simplex or ground return line, is utilized to condition the relay equipment of the link to be controlled over the metallic side of a ground return line or the two sides of a simplex line in parallel. These line circuit relays, when operated in response to seizure of the associated line through one of the connector switches of the system, function to transmit a control pulse back to the connector switch which serves to control the setting of the ringing control equipment provided in the switch in a manner such that the transmission of ringing current over the ground return side or positive talking lead of the associated line is positively prevented. Further in accordance with this feature of the invention, the circuit arrangement of the finder-connector links is such that the ringing control equipment of an assigned link is, in. setting up a reverting call connection involving a line of the ground return type, so controlled from the line circuit terminating the calling line that the possibility of ringing current transmission over the positive or ground return side of the line is precluded.

In accordance with another feature of the present invention, the cut-off and lockout relays embodied in the line circuits terminating the subscriber lines are also arranged to control the ringing control equipment of the links in a manner such that one mode of ring cut-off, i.e.,instantaneous ring cut-off, is provided for terminating the transmission of ringing current over a called line of the full metallic loop type; and another mode of ring cut-off, i. e., silent period cut-off, is utilized to terminate the transmission of ringing current over a called line of the simplex or ground return type. More specifically, the circuit arrangement of the finder-connector links is such that when the cut-ofi and lockout relays 0f the line circuit terminating a called line operate to transmit a control pulse over the positive talking conductor of the associated line in response to seizure of this line, the back-bridge relay of the link occupied with the call is conditioned to function as a ringing control relay before the call is answered, and to function as a. supervisory control relay after the call is answered at the called substation.

The inter-office trunks forming a part of the system are terminated in repeaters which are accessible to the connector switches of the system, and are arranged to be controlled over calling lines of any one of the three types mentioned above. These repeaters are normally arranged for control over a loop line, and in order to condition the control equipment of a seized repeater for control over a simplex or ground return line, each link circuit is equipped with a relay network which functions, incident to the seizure of a repeater, to transmit a-control signal to the seized repeater, indicating that the calling line is of the simplex or ground return type, Each repeater terminating a restricted trunk is provided with a marking path individual thereto, which serves to identify the restricted character of the associated trunk. These marking paths, together with additional marking paths identifying the restricted subscriber lines, serve jointly to control the link circuit equipment in a manner such that calls from substations arranged for restricted service cannot be extended to the restricted trunks. By virtue of this arrangement,

the restriction as to trunk calls is on an individual trunk basis as contrasted with the trunk group marking arrangements known to the prior art. The advantage of the present arrangement resides in the fact that both non-restricted and restricted trunks may be terminated in the same line groups.

The marking paths individual to the subscriber lines and extending to the contacts of the finder switches are also utilized to control the timing relays of the links. More specifically, a relay network is provided for intermittently transmitting ground pulses over these paths. These ground pulses, as transmitted to a seized link, are utilized to render the conversation and permanent timers ineffective to release the seized link.

The marking path extending from a repeater terminating a restricted trunk to the outlet contacts of the connector switches includes one of two control conductors extending between the repeater and the outlet contacts of the connector switches. In accordance with another feature of the present invention, the control conductor forming a part of the marking path indicating a restricted trunk is also utilized for controlling the trunk selecting operations of the connector switches. More specifically, relay means are provided in th repeater for interrupting the marking path and for connecting the two control leads together incident to the seizure of the repeater by one of the connector switches.

In accordance with another feature of the present invention, the timing equipment common to the finder-connector links is connected with the links over a single control lead, this lead being utilized both as a start lead over which operation of the timing equipment is initiated, and as a control lead over which the timing pulses are transmitted to the links. More specifically, this lead is included in the circuit for energizing the start relay of the timing equipment, the arrangev ment beingsuch a that this' startrelay remains; n

operated-to J prevent the release -ot the timingequipment during 'pulse transmission over ==the control lead to the automatic -'--switching equip mentzgether with -furtherobjects-andadvantages thereofywill best-be understood byreference to the.specification taken in connection with the accompanying drawings,-in which Figures'l to 103* inclusive,- when combined inthe manner illustrated-in Fig. 11, illustrate an automatic telephone system having embodied therein the features oftheinvent-ion brieflyoutlined above.

Morespecifi'cally, Fig. 1 illustrates the line equip"- mentserving two-of' the subscriber linesof the system, the link distributor-,and; in "diagram'- matic -form;one-of the finder switches'at which i theillustratedlin'es terminate; Fig. 2 illustrates a relay network-which is utilized for controlling the-restricted service and timing relays of "the links;'-Figs:3 to-6, inclusive, and 10 illustrate the connector end of'the link comprising the finder.

shown in Fig. 1; Figs? and 8 illustrate the repeater-terminating one of the inter-offic'e trunks of -the-system; and Fig. 9 illustrates, in partially schematic .form',:the timing and tone equipment common tothe link circuits.

Referring now more particularly to the drawings, the telephone lines and automatic switchingpquipment there illustrated may comprise, forexamplaa small exchange, commonly known as a community automatic exchange or .C. A.

which is designed to, serve a suburban area of. limited population and is geographically adjacent a larger city or town served by a central exchanges ,More.specifically,.the exchangesis illus-v trated as being connected witha distant central automatic exchange Ibymeans of .a group of trunksiincludingthe trunk 36. Thistrunk is terminated. in the C. A. A.. exchangein a repeater 30a; The subscriber substations served by the1.automatic switching apparatus illustrated maybe arrangedfor three different classes of service. For example, the line 9, which extends.

onlyto the substationA andterminates in the exchange in a line circuit. I0, .maybe arranged for unlimited central exchange trunk service;and' alsorfor local calls of unlimited duratiom The other. illustrated subscriberline I6, whichter minates in the exchangein the line circuit 20, is

of the multiparty type, this line being arranged to serve the two substations B and C. These two substations. may be arranged for either semirestricted or fully restricted service.-- For examplat-he substations-B and C may be arranged so that. central oflice trunk calls over the restricted trunksare prohibited, but local connections established through the automatic switching equipment of the C. A. X. 'may beheld for unlimitedper-iods. Alternatively, the. subscribers at the substations B and C may be prohibited both from routing calls over the restricted central ofiice trunks, and also from holding local call connections for unlimited periods. The particulart-ype; of serviceprovided'for the various substations -:is determined: by the wiring arrangement: of the; line circuits individual to the lines with which the substations are associated. 'More specifically, *if all :-of the-substationsassociated with-:a particular line. are to be denied central oflicentrunk'. service, the line circuit" terminating 1 :vicled inthe restricted servic'e and time blocki'n adapt- -the automatic 'sWitching---:e

-acter of the associated line. I These-line circuitsm this Imeis provicledwith "an EE' C; marking path eXtend-in-g to tli'--firi'der-E. C; contact mun ane having' res-istance battery'potential appliedthre to'th-rough 'the winding of one of the relays pr common battery-type orof the conventional 'loca battery: type. Similarly;- the line i 5 may be -oi the dull metallic' typ'e =-e1nploying two line con 4 ductorsaor may-be of the-ground return type =utiliZ-iI-lg 'a conductoras- 0ne-side =of :theline and ground as the 2 return side of the liner- In -tll e' illustrated arrangement,- theune 9 is shownas' bei'ng of the-full inetallic-' -type; and the-line :18 Li as 'being of th -ground retu rn type." In order to quipm enti for control overthe linesof-diifcrent typespdifiere wiring-arrangements are utilized in the line ci cuits, th'e' particular type of wiring of ea'ch :ci cuit being determined by a the I particular ch'a are substantially conventional inso far as therelay equipment embodied -therein is concerned-ta Thus, the line circuit-l0 comprises the usual line cut-off and lockout relays indicated :at RlSO RI manual H3, 'respectively. Similarly, theiline circuit Zl'l terminating the line it I is providedwitlm a line relay= Rl-lil, --a cut-01f relay Rlfiii; iand' a slow-to-operate lockout relay El 56]."

The automatic switching apparatus providedin the exchange for setting up connections.between the various lines and trunks terminating thereat; comprises a plurality of finder-connectorlinks each having a contact bank-capacity of 'oneihun dred lines. The illustrated-link is shownas'com-r prising a finder switch I land a connector switchm 4i]; For the purpose ofassigning these linksito';- the use of calling lines in a definite-order, theresza is provided .a distributor 22, preferably. offith'ei'ir preselective type, which is arranged to initia'te -the' 1':

operation of the finder portion of a preselected'l link to search-for a calling line in response tor/1 the application of' groundpotential to the" dis; tributor start lead I15 Since thevfinder switch and the distributor-'22 may be of conventional... construction and wiring arrangement, these switching units havebeen only schematically"il-' lustrated in the drawings. The connector switch this illustrated inFigs. 3, 4, 5, 6 and 9 of the" drawings as being 'of' the well known"Strowger"? type, employing a Strowger switching mechanism i having unrestricted service may route connections to the central ofiice subscribers without the intervention of a toll operator. For example, the tenth level of bank contacts in the connector switch 40 may be reserved for the termination of trunks of the last-mentioned group.

Referring now in greater detail to the connector switch 40, the Strowger switching mechanism of this switch comprises the above-mentioned contact field at which the conductors of the lines extending to the C. A. X. are terminated; a set of Wipers 660 to 663, inclusive, and the usual vertical and rotary magnets 408 and 409, respectively, which are operative in conjunction with their associated ratchet and pawl mechanisms, not shown, to impart vertical and rotary movement to the wiper carriage structure. This mechanism is also equipped with vertical offnormal springs M4, M5, M6 and 468, which perform various circuit control operations described with particularity hereinafter. The switching mechanism further comprises a release magnet 401 which, when energized, permits the wipers of the switch to be returned to vertical and rotary normal in the usual manner; and normal post springs H9 and 468, which are arranged to be moved off normal from the normal positions shown in the drawings in response to elevation of the wipers 660 to 663, inclusive, to one or more predetermined vertical oil-normal positions and perform additional circuit control operations described with particularity hereinafter. The equipment for controlling the vertical, rotary and release magnets of the switching mechanism, and for performing the auxiliary control operations required incident to the setting up of the various types of connections referred to above, includes a pair of line relays R360 and R440 which are normally connected to be energized in series over the two talking conductors of the trunk 326 incoming to the connector switch 40. This equipment further comprises a slow acting hold relay R310, a slow-acting hold slave relay R330, a reverting call relay R3I0, a slowacting control relay R320, a link release relay R340, a switch-through relay R350 of the twostep type, a calling simplex relay R4I0, a battery reversing relay R420, a lock-pulse relay R430, a digit transfer relay R450, a pair of slow-acting pulse controlled relays R460 and R410, and a combined ringing and trunk-hunting control relay R480. Additional control relays embodied in the connector switch and shown in Figs. 5 and 6 of the drawings include a second digit transfer relay R5|0, a slow-to-operate, slow-to-release ring cut-off relay R520, a busy test relay R530, a ring pickup relay R540, a restricted service control relay R550, an alternating current ringing control relay R560, a pair of back-bridge relays R510 and REM, a called simplex relay R620, an idle test relay R530, a slow-to-operate conversation timing relay R640, and a slow-to-operate line-switching relay R650. Selection of the ringing code which is to be utilized in signaling over a called multiparty line is accomplished through the provision of a minor switch 45, which also functions as a conversation timing switch after the ringing period is ended and a talking circuit is established through the connector. This switch also functions to determine the side of a selected line over which ringing current is to be projected in signaling over 2. called multiparty line arranged for divided ringing. More specifically, this switch is of the eleven-point type and includes three wipers I000, IO0I, I002, the usual operating and release magnets I004 and I001, re-

spectively, and off-normal springs I005 and I006. The inter-ofiice trunks connecting the exterminates in the repeater 30, has access to the links of the CAX over a link line 34 which ter- Briefly described, the repeater 30 comprises a pair of line relays minates in a line circuit 3|.

R120 and R850, a slow-acting hold relay R020,

a slow-to-release hold slave relay R830, and a group of control relays R840, R810 and R860, the first two of which are of the slow-to-operate type, and the last of which is of the slow-acting type. The relay equipment of the repeater further includes a battery reversing relay R1I0, a calling simplex relay R130, a slow-acting pulse controlled relay R140, an electro-polarized backbridge relay R150, a line-switching relay R880, and three lock-pulse relays R160, R and R8I0 which are provided for impulse correcting purposes. The various enumerated relays are interconnected by control circuits which are described with particularity hereinafter.

The equipment common to the finder-connector links provided in the exchange includes the usual ringing current generator and a ringing interrupter for interrupting the alternating ringing current in accordance with the various ringing codes. The common equipment also includes tick-tone generating equipment 52, dial and busytone generators 60, a conversation timer 53 and a permanent timer 5|. These four units may be of conventional arrangement and, accordingly, have been only schematically illustrated in the drawings. The control circuits for these units are, however, novel in character and, accordingly, the details thereof have been shown. More specifically, the control circuit for the permanent timer 5| and the tone generator 60 comprises a relay R9 I0 which is so connected and arranged that a single control lead C496 is utilized for the purpose of initiating the operation of the timer 5| and for the purpose of transmitting timing pulses to the various links. Similarly, the control circuit for the tone generating equipment 52 and the conversation timer 53 comprises: a slow-to-release start relay R920 and a pulsing relay R930, these relays being so connected and arranged that a single lead C619 is used for initiating the operation of these two units and for the purpose of transmitting timing pulses to the link circuits.

The equipment common to the links and line circuits further includes the restricted service and time blocking relay network 25. Briefly described, this network includes a plurality of line relays R240, R250 and R260, which are individual to the lines with respect to which restricted service or time blocking is required, and a plurality of slow-acting relays R2 I0, R220 and R230, which are common to the lines with respect to which such service restrictions are imposed.

LOCAL CALLS the receiver provided at the substation A from.

ifsrsupporting .hook or. cradle, thereby .to complete a-circuit for energizing the line relay;RI 30 in the usual manner. The circuit over which this line relay is energized is different, depending upon the wiring arrangement utilized in the line circuit l0. Thus, if the substation equipment provided at the substation A is wired for simplex .control of the automatic switching equipment provided in the exchange, the terminals I43 and I4! are connected together, and the terminals -I44 and I45 are connected together. If the line 9 is of the loop or ground return type, or is of sthe-simplex type and the loop resistance thereof isless than 3500 ohms, the relay RI30 is equipped with windings each having a resistance of 200 .ohms. If the line is of the simplex type and the loop resistance thereof exceeds 3500 ohms, the relay RIM! .is equipped with windings each .having a resistance of 1200 ohms. When the above-described wiring arrangement is used, one branch of the operating circuit for the relay R138 extends from ground through the springs of the hook switch provided at the substation A by .wayof the positive line conductor 5b, the contacts I22, the strapped terminals I45 and I44, the lower winding of R938 and the strapped terminals I 41 and I46 to battery. The other branch -of this circuit extends from ground through the springs of the hook switch provided at the substation A by way of the negative line conducor 9a, the contacts I2I and the upper winding of RI30 to battery. On theother hand, if the equipment provided .at the substation A is arranged for loop control of the automatic switching apparatus provided in the community exchange, the terminals I43 and I44 are strapped and the terminals J41 and 148 are strapped. With this wiring arrangement, the operating circuit for the line rely Ri3Il may be traced as extending from ground by way .of the strapped terminals I43 and I44, the lower Winding .oi RISII, the strapped terminals I41 and I43, the contacts I22, the conductor 8b, the bridge across the conductors 9b and 9a at the substation A, the conductor 9a, the contacts IZI and the upper winding of RI30 to battery. In order more completely to describe the different wiring arrangements of the line circuits, it is pointed out that if the line I6 is of the simplex type or is a relatively short ground return line, the line circuit is wired in the manner described above with reference to the line circuit Ill in considering simplex control of the line relay RISlJ. More specifically, in this case the terminals I (iii and .18 are strapped, the terminals I9lland I9I are strapped, and the .termianls 186 and 187 are strapped. On the other hand, if the substations served by the line I3 are arranged for loop circuit control .of the automatic switching equipment, the terminals lab and Hal are strapped, the terminals I84 I85 are strapped, and the terminals I83 and .5 39 are strapped. ,As a further alternative, if the line I6 is of the ground return type, a wiring arrangement is utilized which comprises the strapping of the terminals I all and 1.82, I83 and I35, lSSand I81, and I9!) and 19!, respectively. ill 1th this wiring arrangement, the relay R lfi is energized over a circuit including the grounded conductor lBa, the contacts lfil .the two windings of mm in series when a call initiatedat one of the substations B and C.

Continuing now with the operation of the line circuit Ill, when the line relay RI3 i energized over any one of the circuits traced above, it operates to complete, at its contacts I.3.I, an obvious circuit for impressing ground potential upon the private conductor 9 thereby to mark the-line!) as busy in the bank contacts of the connector switches. At its contacts I32, the relay RI3I] opens the circuit for energizing the cut-off relay RI2IJ when the line 9 is seized through the connector end of one of the links. At its contacts I33, the relay RI30 completes a path including the winding of the relay RI20 and the contacts I I2 for impressing negative battery potential upon the marking conductor 9d, thereby to-identify the line 9 as a calling line in the bank contacts of the 'finder switches having access thereto. At its contacts I34, the relay RI30 completes a path includingthe contacts II4 for impressing ground potential upon the distributor start lead II. When this lead is grounded, the control equipment of the distributor 22 operates in a well- .known manner to cause the finder portion of a previously assigned link to seize the calling 1ine -9. Assuming that the link illustrated, namely, that comprising the finder switch I I and the connector switch 40, has previously been selected for use by the distributor .22, the wipers of the finder switch II are first elevated to a position opposite 'the level of contacts terminating the line 9 and are then rotated to engage the contacts terminatin the conductors 9a, 9b and 901. When the line 9 is found in this manner by the finder switch I I, the control equipment of the finder switch operates to extend the calling circuit through to the connector portion of the link and to connect the marking lead M to the control conductor 3260 of the trunk 326 incoming to the connector'switch' ll). In response'to this cutthrough-operation of the finder switch I I, both of the line relays R350 and R440 are energized. As-

suming thatthe line 9 is arranged for loop circuit control of the automatic switching equipment,

the relays R440 and R360 are energized in series over a circuit which extends from ground byway of the winding of R444), the contacts M3 and 423,

.the repeating coil winding 403, C55, the contacts 354 and 3I2, the trunk conductor 32%, the posi- 'tive line wiper of the finder switch II, the conductor 9b, the bridge across the conductors of the line 9 at the substation A, the conductor 9a, the negative wiper of the finder switch II, the conductor 326a, the contacts 3! I and 352, C63, the repeatin coil winding 4!, the contacts 42I, C64 and. the winding of R330 to battery. When energized overthis circuit, both of the line relays operate. In the event the line 9 is arranged for simplex control of the automatic switching equipment, the line relay R363 is initially energized over a circuit extending from groundat the substation A by way of the conductor 9a, the negative line wiper ofthe finder switch I I, the conductor 326a, the contacts 3 and 352, C63, the repeating coil winding-4M, the contacts 472L064 and the winding of R360 to battery. The other line relay R440 is energized in parallel with the positive side of the line 9 and in series with the lower winding of the line relay RI30 over a circuit which extends from ground by way of the winding of R440. the contacts 3 and 423, the winding 403, C65, the contacts 354 and 3I2, the conductor 326b, the positive line wiper of the finder switch II, the contacts I22, the strapped terminals I44 and I45, the lower winding of RI30 and the strapped terminals I41 and I45 to battery. It will further be noted that in the event the calling line is of the ground return type, the relay R440 is energized in series with the lower winding of the line relay RI 30 over the circuit just traced.

The relay R440, in Operating, closes its contacts I to prepare the operating circuit for the digit transfer relay R450. At its contacts 443, the relay R440 completes a locking circuit for itself which extends to battery through the resistor M8, the off-normal springs 4H and the winding of the release magnet 401. The resistance value of the resistor 418 is such that the release magnet 401 is insufliciently energized to operate when this circuit is completed. At its contacts 442, the relay R440 opens a point in one of the paths for short-circuiting its own winding. At its contacts 444, the relay R440 opens a point in the operating circuit for the callin simplex relay R4l0. The line rela R360, upon operating, closes its contacts 36! to complete a circuit for energizing the lock-pulse relay R430, this circuit extending from ground by way of the contacts 342, 325 and 36l, C15 and the winding of R430 to battery. At its contacts 363, the relay R360 prepares a holding circuit for the hold relay R310. At its contacts 362, the relay R360 opens a point in a priming circuit for itself.

The lock-pulse relay R430, upon operatin locks to ground over a path including C15, the contacts 36I, C91, the contacts 433 and the resistor 428. At its contacts 43l the relay R430 opens a point in the common portion of the circuits over which the vertical magnet 408, the rotary magnet 409, the operating magnet I004 of the minor switch 45 and the relays R460 and R410 are energized during the transmission of impulses to the connector switch. At its contacts 432, the relay R430 completes a circuit for energizing the slow-acting hold relay R310, this circuit extending from ground by way of the contacts 342, ON, the contacts 432, C83 and the winding of R310 to battery.

The relay R310, upon operating. closes its contacts 311, to complete the operating circuit for the digit transfer relay R450, this circuit extending from ground by way of the contacts 342 and 31 I, C11. the contacts 44!. the off-normal springs 468 and the winding of R450 to battery. At its contacts 31l, the relay R310 also prepares the operating circuit for the line switching relay R650 and additional operating and locking circuits described more fully hereinafter. At its contacts 312, the relay R310 completes a path including the contacts 342 for impressing ground potential upon the release conductor 32 60, there-- by to prepare certain locking and operating circuits subsequently referred to in detail. When round potential i applied to this conductor, a holding circuit is provided for the cut-through relay of the finder switch I I, the slow-acting control relay R320 is energized over an obvious circuit, and the cut-off relay R120 is energized over a circuit including this conductor, the test wiper of the finder switch and the contacts I33 and H2. At its contacts 313, the relay R310 further prepares the above-mentioned priming circuit for the line relay R360. At its contacts 314, the relay R310 prepares an operating circuit for the idle test relay R630. At its contacts 315, the relay R310 completes an obvious circuit for energizing the slow-acting hold slave relay R330, At its contacts 316, the relay R310 opens a point in a path traced hereinafter, over which ground potential may be impressed upon the positive line wiper 661 of the connector switching mechanism.

The digit transfer relay R450, upon operating,

locks to ground over a path including the offnormal springs 468, the contacts 453, C1! and the contacts 31l and 342. At its contacts 454, the relay R450 prepares an alternative locking circuit for itself. At its contacts 451 and 458, the relay R450 prepares the above-mentioned circuit for energizing the vertical magnet 408 and the pulse controlled relay R410 in parallel. At its contacts 452, the relay R450 opens one of the alternative circuits for energizing the pulse controlled relay R410. At its contacts 455, the relay R450 opens a point in one of the operating circuits for the pulse controlled relay R460, At its contacts 451, the relay R450 prepares one of the operating circuits for the trunk-hunting relay R483. At its contacts 459, the relay R450 opens a point in the common portion of the operating circuits for the rotary magnet 400 and the operating magnet I004 of the minor switch 45. At its contacts 451', the relay R450 prepares a circuit for energizing the calling simplex relay R4 l 0. At its contacts 458', the relay R450 opens a point in the circuit for transmitting busy and tick-tone currents over the calling end of the connection. At its contacts 459', the relay R450 completes a circuit for transmitting dial tone current over the calling end of the connection. The circuit traversed by the dial tone current may partially be traced as extending from the ungrounded terminal of the dial tone generator by way of C468, the contacts 453', the condenser 445, the contacts 461, C92 and the repeating coil winding 402. This current is, by induction, repeated through the windings of the repeating coil to the calling circuit and is reproduced by the receiver provided at the calling substation to indicate that the dialing operation may be started.

The hold slave relay R330, upon operating, completes a multiple path for impressing ground potential upon the release conductor 3260, this path including the contacts 342, 3l6 and 335. At its contacts 334, the relay R330 opens a point in the operating circuit for the reverting call relay R3|0. At its contacts 33l, the relay R330 prepares the above-mentioned path for impressing ground potential upon the positive line wiper 66l of the connector switching mechanism, At its contacts 333, the relay R330 prepares a path for short-circuiting the conversation timing relay R640 and the lower winding of the link release relay R340, and prepares another operating circuit for the busy test relay R530. At its contacts 336, the relay R330 prepares a locking circm't for the link release relay R340. At its contacts 332, the relay R330 completes a circuit for energizing the upper winding of the link release relay R340 in series with the upper winding of the permanent timer start relay RSIO, this circuit extending from ground through the upper winding of R9l0 by way of the combined time pulse and start lead C496, the contacts 425, C69,

the contacts 332 and the upper winding of R340 to battery. Due to the high resistance of the upper winding of the relay R8l0, the relay R340 does not operate when this circuit is completed. The relay R010, however, operates to complete an obvious path for grounding the permanent timer start lead 55, thereby to initiate the operation of the permanent timer 5| in the usual manner. At its contacts 9|3, the relay R9l0 completes an obvious path for grounding the start lead 56, whereby operation of the dial and busy tone generating equipment 60 is initiated.

The slow-acting control relay R320, upon operating, closes its contacts 322 to prepare the tamer-circuit cas tracedgaboveg andrgopens con- ='tacts.-=44 I eto-zinterruptctha previously traced operating circuit for the digit '.transferrel ay-' R455. t Atwitszcontacts 444;:the relay PAM completes the 1 6 ipreparedsoperating, circuit :for the calling simplex 1ay=3R4 I It, 1 this circuit extending: from ground by ayinofzthmcontactst SE'Ii :and 4M,*the1ower windizringnofi HMO and ithe woiT-norma1- springs 4-l4mto izbattery. wWhenithuswenergized; the calling simcontacts 323, 355 and 363, and therwindingof hplexrelayR4I0;oper.atesandlocks'tothe grounded RIilil: torib'attery. 1 At= its -vcontactsii324 the :relay :R-3.2!l ope ns arpoint in the commortportion-of the operatingicircuitsz for the release magnets Attend l. ADM. .eAtqits :contaets r32 5,. the -'relay-\ R32 intera ruptsithei-previou sly traced operating acircuit :tor

the. lock-pulse relayiRflfl. *liol-lo-wingrthe opera- :tion ofthe relaysRHfiEyRMfi, 3430;3450, R310, c3330 and R320.in;the manner just-explainechno l r further; .operationof the-link circuit :equipment e =occurs= :until i the dialing "operation is ":started ,-at.;

..-the calling substation or the: flinksisa forcibly reeleased under 1 the control of wthe .-.:permanent Jfimel' I When the cut-cit relay.\R.I;20,-is. -energized,.\ it

o operates Jocks to. the :grounded release conductor ;.-lay R120; disconnects the windings-iof the linetreidlayrRiiiwfrom theconductors-of the line 9,-thereby toclear the lineioftthe impedancerepresented by these windings. 'iAt itsflcontactszit l the relay RI 23. a'1so :i-n-terrupts; the npreviously traced. op-

-: crating circuit :-for ;theline relay; R44 I assuming tithe-line- 9. G0'b8-0f-the sin'iplexaor, ground return type. When the line relay'lRilfiilsisithus ldeen- ,ergized, it restores te -interrupt, at its contacts .-aI.3I,.\the-.initia11y completed path for. grounding-1 the privateconductor. Bc of thec1'inea9v. Atvsits contacts xl32',1,the srelay R-ISU. completes an alter ---native .path for impressingground:poten-tialeupon .this,private- -conductor, which path. extends .:-through the contacts I124. rto sthe grounded =testi 5 wiper; of the-:findersw-itch-I i. At; its contacts .3 3, the relay R I39 interrupts: the operating circuitfor the. rout-off relay- RIJEU. eAteitsicontacts e -I-34,,--the relayQ5113!)-v disconnects the. distributor "starts lead I l fromiground andsopens a-peintt in 1 the docking circuit for; the: lockout relay R III].

1 Intheevent theline 9 isof the-ground return ,-=or.simplex.type-; a-path including-the make con- I :tacts.- I 23 ofnthe cut-off .relay vRzl 20.,tand .theibreak contacts I I I ofithe lockoutrelayRI-Iil; is provided i :for transmitting a: control. pulse over the positive --.-talking .conductorBb-and the positive side of the trunk 32%. This control pulse is-utilized tozshort- :-circuit the linetrelay R440. ..-On the other :hand,

-.:if the-line 9 isar-rangedforloep controbofqthe,

.rautomatic switching equipment;v this pulsingpath, ..controlled. "by :the cut-off 's'and. lockout relays inldividual to'the line 9,-isiomitted from the line-cir- .ncuitdfi. When. the; illustrated circuit-wiring is i: provided,the.short-,circuitingwpath just mentioned-i is completed at the contacts I23 when-the cut-:off relay R lzflcperates. 1 This'pathmay be:tracedas -'..exten.ding from, groundgbyway of the contacts I I ;and 1123, 'the positive wiper ofpthe. finder switch .I I the 'trunk ".conductorlr 323b,;rthe contacts: 312' 1ltitsandashortecircuitingvv path for the-relayRti le. At

its. contacts M I; the --relay R llihcompletes the -:second;-1brancht-ofethe circuit for energizing I the .uilinemelayi R3180 oven the '-two sides ofrthe line 9I I "will parallel; in the event-this line is-of the simplex tytpe. wit lore specifically, this second branch may be traced;- .asrextending "from ground at the subr station;.A.-by ways of the line conductor 9b,. .the positive line wiper of. the V-finderswitch I I a the ,-.trunk..conductor[323b, the contacts 3H2 andv354, E65,.the-windineflfl3, the contacts vi123 and M I, C34,-and:the. winding of R330 to -battery. Thus, a the resistance ofW-thescalling icircuit over which =.the linerel ay R3-5Ilis. energizediis materiallyreduced in rresponseuto.operationioflthec'alling. simplextrelay R'lIIl.

iShorrtlynfollowing the operation. of the calll ing simplex .relay'lRdlIiin .the manner pointed outhahove, the) slow-to-operate lockout relay .'.R|.l0 operates and .opens its contacts III, .to ,..inerrupt thejahoveetraced. path short-circuiting'the line re1ayIR440. 'At'its contacts H2, Zthe relayR'i IILopens a further point in the operating..circuit' for the cut-off relay RIZO. -At

its contacts I'l3,the.relay R110 prepares a locking circuitforfitselfh At its contacts I I4, the relay'RI Ii! opens. another .point in the path ior connecting"the distributor start lead I! to ground.

Upon receiving. the. dial. tone signal in the manner pointed out above, the calling subscriber may proceed to..dial the threeidigits of the jdirectory number designating the. desired sub- Hst'atiorr'C. "Theijafirst two of these digits are "utilized to :direct the wipers, of the connector "switch.l iil intoengagement with the contacts "terminatingthe conductors of .the called line '16; iand the' third digit is'utilized to direct the wipers of'fthe' codeyselecting and conversation timing-switch 45' to-the position corresponding to the code designating the desired substation 'C.'JThe-h'ne relayR330 and the lock-pulse relay R 433follow'the'irnpulses of the three digits and "function-to'repeat the impulses of the first digit tothe'wertical magnet 'ttt and the relay R410 "inparal1e1'='-over the above-mentioned pulsing circuit. More'specific'ally-the relay R360, upon "irestoring "at =the- "beginning of each impulse, "-opensits contacts' '3'6l to'interrupt the previous- 'ly -traced-locking circuit for the lock-pulse relay R43II causing' the'latterrelay to restore. At its ':conta'cts 3fi2-, the 1 relay R360 'completes the previously me'ntionedpriming circuit for itself; this "circuit:extendingeby way 'oft 'the grounded hold leadxCilI,i-:the"contacts 323,1.355, 1 362 and' 313, 5. 13118 :resistofif3l1;"C6lg the'conta'cts 4-21; 064' and ethe twir'rding 0f R350'to battery. 'This priming circuit is utilizedwto renderrthe relay R360 -exgeceedinglyfast togoperate-when the calling loop, rsimplexraor single? wire circuit is :recompleted at 2512.440 opensitseontactsntfl to.:interruptsitselockei ithe'z'callingwzrsubstation.;at:the.-tend of the open-- circuit period of the impulse. At its contacts 363, the relay R360 opens the locking circuit for the hold relay R310.

The lock-pulse relay R430, upon restoring at the beginning of each impulse, opens its contacts 432 to interrupt the operating circuit for the hold relay R310. Due to its slow-to-release characteristic, the last-mentioned relay remains operated during impulsing. At its contacts 433, the relay R430 opens another point in its looking circuit. At its contacts 43!, the relay R430 completes the circuit for energizing the vertical magnet 400 and the pulse controlled relay R410, in parallel. This circuit extends by way of the grounded hold conductor C8!, the contacts 323 and 355, C16 and the contacts 43! to the contacts 450 where it divides, one branch extending through the winding of the magnet 408 to battery, and the other branch of the circuit extending through the contacts 45! and the Winding of R410 to battery. When first energized over this circuit, the relay R410 operates to complete, at its contacts 412, an alternative locking circuit for the relay R450, this alternative circuit extending by way of the grounded hold lead 08!,

the contacts 31!, 01!, the contacts 635, C495, the contacts 412 and 454, and the Winding of R450 to battery. At its contacts 41!, the relay R410 opens a point in one of the operating circuits for the relay R460. At its contacts 413, the relay R410 opens a point in the common portion of the operating circuits for the busy test relay R530 and the idle test relay R630. At its contacts 41!, the relay R410 completes an obvious path for short-circuitin the winding 40! of the repeating coil, thereby to reduce the resistance of the pulsing circuit over which the line relay R350 is energized under the control of the calling device provided at the calling substation A. Due to its slow-to-release characteristic, the relay R410 remains operated during each digit and restores shortly after the digit is ended.

The vertical magnet 408, upon operating, elevates the wipers 660 to 663, inclusive, to the first vertical off-normal position and closes its contacts 408, to prepare an alternative operating circuit for the lock-pulse relay R430. In response to this movement of the switch wipers, the offnormal springs 4!4 are opened further to interrupt the operating circuit for the calling simplex relay R4I0, the. off-normal springs 4!5 are closed to prepare or complete a path including the contacts 426 and 442 for short-circuiting the winding of the line relay R440, and the 01T- normal springs 468 are opened to interrupt the operating circuit and the initially completed holding circuit for the digit transfer relay R450. At the off-normal springs M1, the previously traced locking circuit for the line relay R440 is interrupted, causing this relay to restore, if operated. At the off-normal springs 416, the operating circuit for the release magnet 401 is prepared. In restoring, the relay R440 opens its contacts 443, further to interrupt its locking circuit, and closes its contacts 442 to complete the short-circuiting path described above. When this short-circuiting path is completed, the winding of the relay R440 is excluded from the calling loop circuit over which the other line relay R360 is energized, thereby to decrease the resistance of the circuit for energizing the latter relay.

. At its contacts .4!, the relay R440 opens another point in the operating circuit for the digit transfer relay R450. At its contacts 444, the relay R440 reprepares the operating circuit for the calling simplex relay R4!0. From the above explanation it will be apparent that if the line 3 is arranged for loop circuit control of the automatic switching equipment, the line relay R440 is caused to restore and the winding of this relay is excluded from the calling loop circuit in response to the dialing of the first impulse of the first digit of the directory number designating the desired substation.

At the end of the open-circuit period of each impulse of the first digit, the line relay R360 reoperates to complete the above-mentioned alternative operating circuit for the lock-pulse relay R430, this circuit extending from ground by way of the contacts 408, 00!, the contacts 36!, C15 and the Winding of R430 to battery. At its contacts 352, the relay R360 opens the abovedescribed priming circuit for itself. At its contacts 363, the relay R360 recompletes the holding circuit for the hold relay R310. The lockpulse relay R430, upon reoperating, opens its contacts 43! to deenergize the vertical magnet 408 and the pulse controlled relay R410, closes its contacts 432 to recomplete the operating circuit for the hold relay R310, and closes its contacts 433 to recomplete its own locking circuit. From'the above explanation it will be understood that the line relay R360, the lock-pulse relay R430 and the vertical magnet 408 interact in the exact manner just described during each impulse of the first digit. It will further be understood that each time the vertical magnet 408 is energized, the wipers 660 to 663 are elevated one step. Accordingly, at the end of the first digit, these wipers are left standing opposite the level of bank contacts in which the conductors of the called line !6 are terminated.

During the inter-digit pause between the first and second digits, the line relay R360 and the lock-pulse relay R430 are held operated for a time interval in excess of the release period of the slow-acting pulse controlled relay R410. Accordingly, the relay R410 is caused to restore. In releasing, this relay opens its contacts 41! to interrupt the path short-circuiting the winding 40! of the repeating coil, and closes its contacts 41! to reprepare one of the operating circuits for the pulse controlled relay R460. At its contacts 413, the relay R410 reprepares the operating circuits for the busy test relay R530 and the idle test relay R030. At its contacts 412, the relay R410 opens the above-traced alternative holding circuit for the digit transfer relay R450, causing the latter relay to restore.

In releasing, the relay R450 closes its contacts 452 to prepare an alternative operating circuit for the pulse controlled relay R410. At its contacts 45!, the relay R450 opens another point in the initially completed operating circuit for the relay R410. At its contacts 453, the relay R450 opens another point in its initially completed holding circuit. At its contacts 454, the relay R450 opens another point in its alternative holding circuit as traced above. At its contacts 455, the relay R450 prepares one of the operating circuits for the pulse controlled relay R460. At its contacts 458, the relay R450 opens another point in the above-traced circuit for energizing the vertical magnet 408 and the relay R410 in parallel. At its contacts 459, the relay R450 prepares a circuit for energizing the relays R460 and R410 in parallel with the rotary magnet 409. At its contacts 451, the relay R450 opens another point in the incomplete operating circuit for the calling simplex relay R4).

At its contacts 458', the relay R45fl prepares the previously mentioned circuit for transmitting busy and tick-tone currents over the calling end of the connection. At its contacts 59, the relay R450 interrupts the previously traced circuit traversed by the dial tone signal current, thereby to terminate the dial tone signal being reproduced by the receiver provided at the calling substation A. Following the release of the relay R450, the link circuit equipment is conditioned to respond to the impulses of the second digit.

During-the dialing of the second digit, the line relay R360 and the lock-pulse relay R439 cooperate to repeat the dial pulses to the relays R460 and Rim, and the rotary magnet 499 in parallel. More specifically, the circuit over which current pulses are transmitted to these control elements extends by way of the grounded hold lead 03!, the contacts 323 and 355, C16, the contacts 431 and 4593, C494, the contacts 634, 0810 and the contacts 532 and H. to C493 where it divides, one branch extending through the winding of the magnet 489 to battery, and a second branch extending through the contacts 41! and the winding of R430 to battery. A third branch of this circuit extends from the conductor C810 by way of the contacts 53!, C99, the contacts 453 and the winding of R419 to battery. When this circuit is initially completed at the beginning of the open-circuit period of the first impulse of the second digit, the relays R460 and R415 both operate; Upon operating, the relay R410 closes its contacts till to recomplete the path for shcrt-circuiting the repeating coil winding 4M, opens its contacts Hi to interrupt the initially completed operating circuit for the relay R430, and closes its contacts 412 to complete an alternative circuit for energizing the 1ast-mentioned relay. This alternative circuit extends by way of the grounded hold conductor C81, the contacts 3H, CH, the contacts 335, C495, the contacts 412 and 155, and the winding of RQEU to battery. At its contacts 413, the relay R410 again opens a point in the operating circuits for the busy and idle test relays.

The relay R 361), upon operating, closes its contacts 331 to complete a path for short-circuiting the winding of the digit transfer relay R5lil, this path extending by way of the grounded hold conductor C31, the contacts 31 I, CH, the contacts 635, C 595, the contacts 412, 455 and MI, 049i, the contacts 5H9, the winding of REM and the contacts 529 to the grounded release conductor 3260. At its contacts 563, the relay R460 prepares a circuit for energizing the upper winding of the two-step switching-through relay R355. At its contacts dcd, the relay R488 prepares the operating circuit for the busy test relay R538. At its contacts 665, the relay R468 opens a point in the holding circuit for the busy test relay R530. At its contacts 435, the relay R439 opens a point in the operating circuit for the idle test relay R6351. At its contacts 461, the relay R439 opens a point in the path for transmitting signal currents over the calling end of the connection. Due to the slow-to-release characteristics thereof, the relays R410 and R439 remain operated throughout the second series of impulses transmitted to the link.

Each time the rotary magnet 469 is energized, it operates to rotate the wipers 633 to 633, inclusive, one step, and closes its contacts 409 to prepare an alternative operating circuit for the lock-pulse relay R435. This alternative circuit is completed in response to the reoperation oi the line relay R330 at the end of the open-circuit period of each impulse. Specifically, this circuit extends from ground by way of the contacts 433', C3], the contacts 35!, C75 and the winding of R liiil to battery. Each time the lock-pulse relay arse reoperates, it'recompletes its holding circuit in the manner previously explained.

From the above explanation, it will be understood that in response to the impulses of the second digit, the wipers 683 to 663, inclusive, are rotated step by step until at the end of the digit they stand in engagement with the contacts terminating the conductors of the called line Iii. During the inter-digit pause between the second and third digits, the line relay R353 and the lock-pulse relay R 330 remain operated for an interval in excess of the combined release periods of the relays R410 and R460. Upon restoring, the relay Rd'ill opens its contacts 512 to interrupt the locking circuit for the relay R363, and closes its-contacts ill to reprepare the operating circuit for the relay R463. At its contacts 613, the relay R410 reprepares the operating circuit for the busy test relay RbSll. At its contacts E12, the relay R' l'iil also interrupts the above-traced path short-circuiting the winding of the digit transfer relay RENE, permitting the last-mentionedrelay to be energized in series with the relay Rdtil over a circuit which extends by way of the grounded release conductor 3260, the contacts 529, the winding of REM, the contacts 5I3, 043i, the contacts Gill and the winding of R636 to battery. When thus energized, the relay RSI ll operates and locks up in a circuit including the grounded release conductor 32i5c, the contacts 5E2 and the resistor hi9. After this locking circuit is completed, the relay Riiltl opens its contacts M9 to interrupt its operating circult and thus deenergize the relay R 69, causing the latter relay to restore. At its contacts M l, the relay R5! 0 prepares the operating circuit for the ring pickup relay R540. At its contacts 5M, the relay Rfil 0 opens a point in the common portion of the paths for short-circuiting the timing relay REM] and the lower winding of the link release relay R345. At its contacts Elli), the relay R5? prepares an alternative circuit for energizing the busy test relay R539], this circuit only being utilized in providing the restricted service facilities described more fully hereinafter. At its contacts 5|6, the relay Rblll prepares the operating circuit for the restricted service relay R553. At its contacts 5H, the relay Rillll open: a point in the common portion of the abovetraced branch circuits for energizing the relay R l'll in parallel with the rotary magnet 439. At its contacts 558, the relay Rhiil prepares a circuit for transmitting impulses to the operating magnet lilll l of the code selecting and conversation timing switch 45. The release of the pulse controlled relay R4653 in response to operation of the digit transfer relay REM is without effect at this time. v

The impulses of the third digit dialed at the calling substation are repeated by the line relay R360 and the lock-pulse relay RBil to the pulse controlled relay Rt'lil and the operating magnet 5084 of the switch 45 in parallel. In this case, the pulsing circuit extends from the grounded hold conductor C3! by way of the contacts 323 and 355, C16, the contacts 43! and 3553, CAM and the contacts 634 to C310 where it divides,'one branch extending by way of the contacts 53} C99, the contacts 4&2 and the winding of R413 to battery, and the other branch, extending by way of the contacts 532 and 5i8, Gill and the winding of the magnet I004 to battery. When thus energized at the beginning of the first impulse of the third digit, the relay R410 again completes the previously traced circuit for energizing the relay R400. The two relays R450 and R410 remain operated until shortly following the end of the digit. Each time the operating magnet [004 is energized over the pulsing circuit just traced, it operates to step the wipers I000, I00! and I002 one step, and closes its contacts I033 to prepare another operating circuit for the lock-pulse relay R430. When the enumerated wipers of the switch 45 are moved ofi normal, the off-normal springs i005 are disengaged to open a po nt. in the operating circuit for the release magnet 40?, and the ofi-normal springs i030 are moved into engagement further to prepare the circuit for energizing the release magnet I001. In the present case, the lock-pulse relay R430 is energized in response to each reoperation of the line relay R350 over a circuit which extends from ground by way of the contacts 1003, C91, the contacts 36L C and the Winding of R430 to battery. This relay, in reoperating, locks. to ground through the contacts 433 and the resistor 4'28, and opens its contacts 43l to interruptthe pulsing circuit extending to the magnet I004 and the relay R! 010. Thus, the magnet i004 is energized once in response to each impulse transmitted to the link over the calling line. Accordingly, the wipers of the switch 45 are, at the end of the digit, left in the off-normal position corresponding to the code designation of the desired substation.

Busy test At the end of the third digit, the pulse controlled relays R410 and R460 restore in the order named. The operations which occur in response to the sequential release of these relays depend upon the idle or busy condition of the called line Hi. In this regard it will be noted that if this line is idle, the line, cut-off and lockout relays of the line circuit are at normal so that the private conductor 150 of the line I6 is marked with negative battery potential through the winding of the cut-ofi relay RI 30. On the other hand, if the line I0 is occupied with a call, the private conductor I00 is marked with ground potential over a path including the grounded test conductor 15d and the engaged make contacts I04 of the operated cut-off relay RIBII.

Assuming that the called line I5 is busy at the time it is selected in the manner explained above, the relay R410, upon restoring at the end of the third digit, completes the prepared operating circuit for the busy test relay R530. This circuit extends by way of the grounded private conductor I00, the private Wiper 663, C080, the wiper I00l, C00 or C58l and the contacts 531, depending upon the off-normal position occupied by the wipers of the switch 45, C80, the contacts 413 and 45 3,0504 and the upper winding of R530 to battery. When thus energized, the relay R530 operates and closes its contacts 531 to prepare a locking circuit for itself. At its contacts 53!, the relay R530 opens another point in the operating circuit for the relay R413. At its contacts 532, the relay R530 opens a point in the common portion of the operating circuits for the rotary magnet409 and the operating magnet I004. Thus, following operation of the busy test relay R530, the magnets 400, 409 and i004, and the relays R450 and R410 are prevented from responding to further operation of the calling device provided at the calling substation, At, its contacts. 533, the relay R530 opens the prepared operating circuit for the restricted service relay R550. At its contacts534, the relay R530 further prepares the operating circuit for the trunk-hunting relay R400. At. its contacts 53-5, the relay R530 opens a point in the operating circuit for the idle test relay R530, At its contacts 538, the relay R530 prepares a looking circuit for the switching-through relay R350 and a path for connecting the release conductor 3200 to the test wiper 503. At its contacts 530, the relay R530 opens a point in another of, the locking circuits for the switching-through relay R350. At its contacts 531, the relay R530 prepares the circuit'for transmitting busy tone current over, the calling end of the connection. At its contacts 538', the relay R530 -opens a point in the circuits for transmitting ringing current and tick-tone current over the calling end of the con nection. At its contacts, 530, the relay R530 prepares an alternativelocking circuit for the lockpulse reiay R430, which circuit, is utilized only in the event further impulses are inadvertently dialed at the calling substation. Thus, if an additionai digit is dialed at the calling substation after the three digits ofthe directory number designating the desired substation are dialed, the line relay R350, upon restoring at the beginning of the open-circuit period. of, each impulse, opens the locking circuit for the lock-pulserelay R430, causing the latter relay to restore. Thereafter, and when the line relay R360 reoperates, the lock,- pulse relay R430 is energized over a circuit extending by wayof the grounded conductor C8l, the contacts 323: and 355, C10,, the contacts 43l and 459,. C034,. the contacts 634, C370, the contacts 530?, 03!, the contacts 36[ and C15 and the winding. oilR430to battery. Whenthus energized, the relay R430 locks torground through its make contacts 433' and the resistor 428, and then opens its contacts 43l to interrupt the alternative operating circuitzjust traced.

Shortly following the operation of the busy test relay R530 in the manner pointed out above, the slow-actingpulse-controlled relay R460 restores. t itscontacts 435, the relay R460 completes the prepared lockin circuit for the busy test relay R530, this circuit extending by way of the grounded release conductor 3206, the contacts 53?, C585, thecontacts 465, C584 and the upper winding of R530 to battery. At its contacts 40?, the relay R430 completes the repared circuit for transmitting busy tone current over the calling end of the connection, This circuit parallels that traversed by the dial tone current as traced above, but is derived from the busy tone current source over a path including the conductor C543, the contacts 531, C581 and the contacts 450 The reproduction of this signal current by the receiver provided at the calling substation A serves to inform the calling subscriber that the desired line is busy. The manner in which the operated switching equipment is released when the call is abandoned at the called substation is described with particularity hereinafter.

Idle test In the event the called line i0 is idle at the time it is selected, nocircuit is provided for energizing the busy test, relay R530 whenv the pulsecontrolled relay Rflflrestores, the, upper winding of vthe busy test relay being short-circuited in 

